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Star Colour - Questions??? Other · Dominik · ... · 7 · 369 · 6

OnlyTheSky 0.90
Dominik
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Hello,

i have a specific problem with star colors. It seems that I am completely missing blue tones (stars) in the images taken with my ZWO ASI 533MC Pro. The star results are disappointing. The stars appear blurred, more yellow and white.

I have now received some advice that it could be due to the distance to the sensor. Since I do not use N.I.N.A and therefore do not have access to the Hocus Focus tools, I have done analyses with ASTAP and CCDInspector.

Here are a few examples of my recent images, and in addition, I am posting 30s exposures here that are supposed to represent the sensor data. I would be grateful for some help and a few comments.

Equipment:

HEQ5 Pro (RMS was between 0.5 and 0.7 arcsec)
TS-CF APO 480/80mm ( TSCF Red. 0.8 > 384mm FL)
APM 50mm Guidesscope
ZWO EAF
ZWO AAP
ZWO Filter Drawer 
Baader UV/IR Cut 1.25"

Image Train 55mm
TSCF Red0.8 > M48/M42 Adapter 0mm > 16.5mm ZWO Adapter > ZWO Filterdrawer (1.8-2mm Filter DNB/UV-IR) 21.0mm > > 17.5mm (6.5mm Sensor + 11mm Adapter Ring) > +- 0.65 - 0.-85mm (Filter)

To ensure the distance due to the thickness of the filter, I conducted tests over 2 days with distances of 0.65mm and 0.85mm respectively

Thank's for help. 

CS
Dominik

Example edited Images:

Rosette Nebula
Bubble Nebula
Veil Nebula
Horsehead

10.01.2024 / +0.85mm (30s Exp. / NGC663)

CCDInspector
image.png

image.png

image.png


11.01.2024 / +0.65mm (30s Exp. / NGC663)

image.png

image.png

image.png
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JanvalFoto 4.51
Jan Erik Vallestad
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Are the stars round all across the frame? If so, I wouldn't worry. Those ASTAP graphs tend to vary a lot even between subsequent frames and relies on seeing etc as well. At least that's my experience, I went from "severe tilt" to "no tilt" by using test shots taken during better seeing.

Regarding star color I noticed several of your sub lengths are probably far too long and the stars are over-exposed. IF you want tight and colorful stars I would try to reduce the exposure to 30s or maybe even less just to get the stars.
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jakicevichap 0.90
Matija Jakičević
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What I do in Pixinsight, not sure if there's a free equivalent to blurx, is:

After DBE (background extraction) and color correction I blurx the image with "correct only" first to clean up star shapes and aberration, and then blurx it again without sharpening stars to target nebulosity. Separate the stars from the image using Starx (you can use starnet, but watch out for small details subtracted). Then I process the nebulosity by itself, stretching, denoising and saturating it as well.

Now onto the stars. What I do is reduce the level I stretch the stars to as this reduces the size of the stars without creating artifacts (don't overdo this step). Stretch them, then I do a single pass of saturation, remove green noise using SCNR (use siril equivalent) and saturate again.

At this point your blue stars will most likely have a magenta tint, to get rid of that what I do is invert the image and run the SCNR process for green noise (magenta inverted becomes green). Invert the stars back and you should have a pretty clean and colorful star field. Screen the stars back in and gg.

Every project is different, but that's the gist of what I do. I could be wrong though so feel free to let me know if there's a better way to do this…

CS,
Matija
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OnlyTheSky 0.90
Dominik
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Are the stars round all across the frame? If so, I wouldn't worry. Those ASTAP graphs tend to vary a lot even between subsequent frames and relies on seeing etc as well. At least that's my experience, I went from "severe tilt" to "no tilt" by using test shots taken during better seeing.

Regarding star color I noticed several of your sub lengths are probably far too long and the stars are over-exposed. IF you want tight and colorful stars I would try to reduce the exposure to 30s or maybe even less just to get the stars.

Hi,
the stars are actually very good and round across the entire image. I have a extreme minimal tilt in the top right corner of the image. It seems ok for me.

Except for the Rosette Nebula, for which I only captured RGB, all other images were taken separately. First RGB, then Duo Narrowband. I kept the exposure times for the RGB Star captures relatively short 30-60s. 

Just take a look at my gallery. I've provided the integration time and Filter.

Gallery

Could it be that I simply need more integration time?

I understand that tools like ASTAP or CCDInspector also depend on the seeing conditions. I was thinking more about the correct sensor distance.

CS
Dominik
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OnlyTheSky 0.90
Dominik
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Matija Jakičević:
What I do in Pixinsight, not sure if there's a free equivalent to blurx, is:

After DBE (background extraction) and color correction I blurx the image with "correct only" first to clean up star shapes and aberration, and then blurx it again without sharpening stars to target nebulosity. Separate the stars from the image using Starx (you can use starnet, but watch out for small details subtracted). Then I process the nebulosity by itself, stretching, denoising and saturating it as well.

Now onto the stars. What I do is reduce the level I stretch the stars to as this reduces the size of the stars without creating artifacts (don't overdo this step). Stretch them, then I do a single pass of saturation, remove green noise using SCNR (use siril equivalent) and saturate again.

At this point your blue stars will most likely have a magenta tint, to get rid of that what I do is invert the image and run the SCNR process for green noise (magenta inverted becomes green). Invert the stars back and you should have a pretty clean and colorful star field. Screen the stars back in and gg.

Every project is different, but that's the gist of what I do. I could be wrong though so feel free to let me know if there's a better way to do this...

CS,
Matija
#

I think i'll have to buy PixInsight in the near future. There are simply more options and information. Thanks for the comment.

I'll try the tip with the stars. 

Thank you!

CS 
Dominik
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jakicevichap 0.90
Matija Jakičević
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Dominik:
I think i'll have to buy PixInsight in the near future


It's a very good investment for a stable processing workflow. Invest a bit more into ai software by RC and you'll get even better. If you have to pick one go for BlurX.

Good luck and let me know how it goes!

Cs,
Matija
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andreatax 9.89
andrea tasselli
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Your images have a very poor color contrast because of the way you process them (they look monochrome i.e., mostly red tones) and that is glaring evident in the Rosetta nebula which should should show plenty of blueish tones which are however essentially absent. The scope you use also does you no favors as the bloating seems pretty pronounced (in fact I recall I went for the f/7.5 version of the same lens because of the poor color correction).
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OnlyTheSky 0.90
Dominik
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andrea tasselli:
Your images have a very poor color contrast because of the way you process them (they look monochrome i.e., mostly red tones) and that is glaring evident in the Rosetta nebula which should should show plenty of blueish tones which are however essentially absent. The scope you use also does you no favors as the bloating seems pretty pronounced (in fact I recall I went for the f/7.5 version of the same lens because of the poor color correction).

Hi,

i think it's unlikely to be an issue with the telescope. The TS-Optics CF-APO 80 mm f/6 Triplet with FPL55 usually has good color correction. 
When I look at my first image of M101 taken with a DSLR with a built-in UV/IR filter, the blue of the stars looks much better. In general, there's simply more blue present.

M101
APO Specs
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